The present invention relates generally to hypodermic injection devices, and more particularly to a gas pressurized, single-use needleless injection device or syringe that avoids piercing the skin by utilizing a high pressure jet to pass a medication or other substance through the skin.
In the medical profession, it is known to administer needleless medication injections through the use of "permanent gun" instruments which are generally referred to as "jet injectors". These prior art devices typically employ the use of either a compression spring or a compressed inert gas to propel fluid medication via a push rod plunger through a small orifice or opening of an injector nozzle. The injector nozzle is pressed directly against the injection site in perpendicular relation thereto, with the fluid medication generally being accelerated at a high rate of speed of between about 800 feet per second and 1,200 feet per second. This rate of speed causes the fluid medication to pierce through the skin's surface without the use of a needle, thus resulting in the fluid medication being deposited in a flower-like pattern under the skin's surface. This method of medication delivery is typically referred to in the medical profession as a subcutaneous injection. The jet injectors and similar needleless injection devices are generally perceived as reducing the relative risk and discomfort of puncturing the epidermis with a hypodermic needle, and being more easily used by persons of limited skill. Thus, the use of such devices has become of increasing interest, particularly by users such as those requiring frequent insulin injections.
Conventional jet injectors as known in the prior art are often cumbersome and awkward to use, with the preparation of a typical, reusable jet injector for administering an injection requiring several steps. More particularly, prior to each injection, the injector nozzle must be sterilized. To satisfy this need, the user removes the injector nozzle from the jet injector and boils the nozzle in water to assure a reasonable degree of sterilization. After the injector nozzle has been cleaned and sterilized, the user replaces it on the jet injector and prepares the same for loading the medication which is to be injected into the skin. A concern often associated with the injector nozzle in the prior art reusable jet injectors is that due to the relatively small opening (approximately 0.004 inches or less), the nozzle has a tendency to clog if the jet injector is left unused for a period of time or if the user does not clean the nozzle each time after its use and prior to its reuse.
A further deficiency of prior art jet injectors is that loading the same with fluid medication is typically a time consuming and delicate operation. In a typical loading procedure, an adaptor which contains a needle is first placed through the rubber septum of a medication vial. The injector nozzle of the jet injector is then mated or coupled to the adaptor, with the user then proceeding to draw medication into the delivery chamber of the jet injector. This operation may repeated several times, until the trapped air in the delivery chamber is removed. When this pre-injection operation is complete, the user selects an injection site on the skin and administers the injection.
However, a used and worn delivery orifice of the injector nozzle can slow down the delivery speed of the injected fluid medication, thus resulting in inadequate penetration and bruising of the skin at the injection site. Additionally, the improper use of jet injectors creates bruising (subdermal hematoma) when the injector nozzle is not firmly pressed against the skin at the injection site. Bruising may also occur if the orifice or opening of the injector nozzle is partially clogged or worn out.
With regard the prior art jet injectors employing the use of a compression spring, such compression spring propelled jet injectors are typically considered deficient in that they do not offer linear delivery speeds, i.e., a constant speed of the fluid medication being injected. Moreover, spring propelled jet injectors with weak or deteriorated springs often slow down the delivery speed of the fluid medication while the same is being administered into the skin which can result in improper fluid penetration. Reduced speed of the fluid medication delivery can also cause improper dosing and bruising at the injection site.
In recognition of the aforementioned deficiencies of jet injectors, there has been developed in the prior art single use needless injection devices or syringes, with one such injection device being described in U.S. Pat. No. 4,913,699 issued to Parsons on Apr. 3, 1990 which is owned by the Applicant. More particularly, the Parsons reference discloses a pre-sterilized disposable, single-use injection device which has its own compressed gas power source and is small and light enough for the user to carry the device along during the day. The Parsons injection device is adapted to be filled with a selected dosage of fluid medication from existing medication vials, and is operable without the need to cock a spring due to its use of compressed gas as the source of power.
Though the Parsons injection device overcomes many of the deficiencies of the prior art jet injectors, it possesses its own deficiencies which detract from its overall utility. More particularly, the configuration of the trigger mechanism of the Parsons injection device makes it susceptible to accidental discharge during manufacture/assembly and transport, in addition to increasing the complexity of the manufacturing and assembly process and hence the cost thereof. Moreover, the Parsons injection device lacks a quickly and easily discernable visual indicator that the compressed gas power source has been discharged. Also, the Parsons injection device is not well suited to being pre-filled with a fluid medication since it is neither outfitted with structures or fabricated from materials which are adapted to extend the shelf life thereof by maintaining the bioavailability of the fluid medication, or reducing leakage or out-gassing of the pressurized gas.
The needleless syringe constructed in accordance with the present invention is a single unit, single use syringe which is non-reusable and completely disposable, thus minimizing its susceptibility to contamination. The present needleless syringe overcomes the deficiencies of the Parsons injection device by providing a trigger mechanism specifically configured to facilitate the manufacture, assembly, pre-filling and transport of the syringe with substantially reduced susceptibility to accidental actuation or discharge. Additionally, the present needleless syringe may be provided with internal liners or sleeves specifically adapted to increase the shelf life thereof by substantially reducing the potential leakage of pressurized gas therefrom and/or maintaining the bioavailability of the fluid medication by preventing a derogatory interaction between the fluid medication and the syringe material or protecting the fluid medication from exposure to air and/or sunlight (i.e., ultraviolet radiation) if photosensitive. The present needleless syringe may be provided with an external reinforcement sleeve which allows for the fabrication of the syringe from lower strength materials specifically suited to maintain the bioavailability of the fluid medication. Various coatings may also be applied to distinct sections of the interior of the needleless syringe which change colors when exposed to the pressurized gas for purposes of providing a clear visual indication that the same has been discharged. These, as well as other features and advantages of the present invention, will be discussed in more detail below.